The present invention relates to a process for treating the surface of a solid containing ruthenium, osmium or their oxide by etching. Furthermore, the present invention relates to a process for producing a semiconductor device, particularly to a process for etching treatment and cleaning treatment of said metal or its oxide formed above a substrate and also relates to a process for cleaning a CVD reactor or an etching reactor used in the foregoing processes.
With recent higher integration of semiconductor devices, devices with memory cells such as DRAM, etc. will have more and more complicated spatial structures to ensure a condenser capacitance. Consequently, number of steps for device production is increased and a margin for thin film formation and processing is narrowed, thereby increasing the production cost and lowering the yield. Thus, it is essential for an increase in the condenser capacitance to use novel high-dielectric materials to simplify the structure.
Double oxides such as BaSrTiO3 are now under study as such high dielectric materials. It is necessary to conduct high temperature annealing in an oxygen atmosphere during the formation of these oxides. However, in case of using Si as a condenser lower electrode material, it is hard to suppress an increase in the resistance due to oxidation during the oxygen annealing, and thus it is necessary to use scarcely oxidizable novel materials or materials which have a good electroconductivity even if oxidized.
As electrode materials which can satisfy these conditions, for example, ruthenium and ruthenium oxide are now under study.
As a process suitable for forming these electrode materials, a CVD (chemical vapor deposition) process has been proposed, which can produce a thin film of high purity and distinguished crystallinity with a good thin film depositability onto a substrate relative to the physical vapor deposition.
Processes for forming a thin film of ruthenium or ruthenium oxide by MO-CVD using specific organic feed gases are disclosed, for example, in JP-A-6-283438 and JP-A-9-246214.
As to processes for forming a thin film of ruthenium or ruthenium oxide by etching, on the other hand, a process for producing a semiconductor device, which comprises a step of plasma etching using a gas mixture comprising at least one member selected from the group consisting of a halogen gas comprising at least one of fluorine gas, a chlorine gas and an iodine gas and hydrogen halides, and an oxygen gas or an ozone gas is disclosed, for example, in JP-A-8-78396.
Furthermore, a process for obtaining pure ruthenium tetraoxide by reaction of ruthenium with ozone at room temperature is disclosed by Rainer Loessberg and Wrich Mueller in Zeitschrift fuer Naturforschung, Section B, Chemical Sciences, vol. 16B, No. 3, 1981, pp 395.
Still furthermore, as to a technique of removing ruthenium residues, a wet cleaning process using a cleaning solution comprising periodic acid and nitric acid is disclosed in Japanese Patent Application No. 11-245143.